Stack Coins for Integer Action!

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Positive and negative whole numbers, called integers, can pop up anytime, anywhere in middle school math. Understanding how to add and subtract integers can be a challenge at first, but once you know how to handle the heat, it's a breeze! Remember when your middle schooler was a kindergartener and learned 2+2=4 using Cheerios? The same idea can be used with integers, however the Cheerios are now coins and the process requires a couple more steps!

What You Need:

10 pennies

10 nickels

3 penny-nickels (3 pennies stacked on 3 nickels)

pencil

paper

What You Do:

Now that you've got adding integers covered, it's time to subtract!

Place 10 pennies and 10 nickels on the table. Explain that the pennies represent positive integers and the nickels represent negative integers. If it helps - think P (pennies) for positive and N (nickels) for negative.

Write a simple addition problem using integers: -3 + 5=

Place 5 pennies in a line and below that put 3 nickels in a line.

P P P P P

N N N

Place the 3 nickels on top of 3 pennies. Explain how positive and negative integers cancel each other out, and ask, “What do you have left?” (Answer: 2 pennies, or positive 2)

Repeat the process using different addition problems:

(2) + (-6) =

P P

N N N N N N

Place 2 pennies on top of 2 nickels. Ask “What do you have left?” (Answer: 4 nickels, or negative 4)

(-2) + (-6) =

N N

N N N N N N

In this case, point out that there are no pennies (positives) to cancel out the nickels (negatives), so you can just add up the nickels. (Answer: 8 nickels, or negative 8)

Set up three more nickels with a penny on top of each. (You'll have a total of 13 pennies, 13 nickels on the table.) Emphasize again how positive and negative integers cancel each other out - so these penny-nickel stacks equal zero!

Subtracting integers is all about changing the signs first. For example:

4 – (-1) becomes 4 + (+1)

Show this with the coins by placing four pennies down, then include one penny-nickel.